Plastic injection molding machines and systems are in common use today. The majority of plastic products and components that are in use today are made by plastic injection molding processes. In plastic injection molding systems, an injection molding machine melts plastic material and then injects the molten plastic material through a machine nozzle into a mold cavity. Typically, a hot runner manifold or system and a plurality of sprue bushings are positioned between the machine nozzle and the mold cavity. The hot runner manifolds distribute the molten plastic material from the machine nozzle through the sprue bushings and into multiple cavities in the mold or into different areas of a large cavity in a mold.
In a typical injection molding process, the molten plastic material injected into the mold cavity is allowed to cool and harden sufficiently so that it can be removed or ejected from the mold. In a typical plastic injection molding cycle, the plastic material is first injected into the mold cavity, the plastic material is allowed to cool and harden for a predetermined period of time, and then the mold is opened, allowing the molded part to be removed or ejected. Subsequently, the mold is closed and the cycle is repeated. Typically, the cycle is repeated over and over throughout a work shift or several work shifts until the requisite number of molded plastic parts are produced.
In some plastic injection molding processes, it is necessary to retract the machine nozzle from the hot runner manifold between the processing cycles. This can occur, for example, with rotary molds and stack molds. In these molding processes, when the machine nozzle is retracted, it is necessary to prevent the backflow of plastic material from the manifold which could affect subsequent processing cycles or produce substandard molded parts.
Several shutoff nozzles or mechanisms have been provided in the past in order to prevent such backflow of molten plastic material from hot runner manifolds. However, not all of the shut-off valves have been successful, and many do not have universal applications or are not able to be easily modified for different applications.